Electric or hybrid machines are widely used as alternatives to their mechanical counterparts in industrial applications due to their higher efficiency and lower maintenance requirements. These machines typically contain high-voltage electric loads. Large charge-storing devices are usually included to stabilize the high-voltage power system. During normal operation these charge storing devices may be capable of storing several thousand volts of potential energy. The charge-storing devices may store high-voltage charges for substantial amounts of time, even when the machine is powered down. Thus, it may be desirable to detect a high-voltage condition associated with an electric or hybrid machine and provide a warning signal indicative of the high-voltage condition.
Furthermore, it is also important that the indication system is reliable, in particular, the system is desired to have a low false alarm rate. Self-test and diagnostic functions are therefore desirable features of the indication system, to minimize the possibility of both a missing alarm and a false alarm due to malfunction of the indication system.
Yet another factor to consider in the design of the indication system is cost-effectiveness. Since low-power dissipation components are usually available at lower cost, it is generally desirable to use low power dissipation components.
One system for detecting the voltage level of a power source is described in U.S. Pat. No. 6,885,215 to Hou et al. (“the '215 patent”). The '215 patent describes a voltage detector circuit with a programmable threshold point. The detector includes a voltage following circuit connected to a power source for tracking the voltage value of the power source, and a selectable threshold point circuit connected to the voltage following circuit to provide the threshold value. The voltage detector described in the '215 patent is configured to generate an output indicative of whether the value of the power source has increased above or decreased below the threshold value. In one instance, the threshold point is established by the amount of current provided by the threshold point circuit, which may further be determined by the size and type of transistor used in the selectable threshold point circuit.
Although the voltage detection circuit described in the '215 patent may be effective for detecting voltage levels, it may be problematic. For example, the system described in the '215 patent may lack reliability. That is, because the detection circuit of the '215 patent operates exclusively from a primary power source, it may be incapable of operation in the event of a power failure. As a result, equipment systems that rely on continuous voltage detection even in the event of loss of power may become inoperable. Further, the voltage detector disclosed by the '215 patent may lack reliability for the additional reason that it does not provide self-test functions or diagnostic functions, and isolation.
Furthermore, the solution provided by the '215 patent may not be cost effective. For example, in a high-voltage system, the voltage level of the primary power source is usually high as well. Directly powering the entire detection circuit from such a high-voltage source requires high-power dissipation components, which are typically more expensive than low-power dissipation components.
In addition, the system described in the '215 patent may provide insufficient isolation between the detection circuitry and the processor circuitry. As a result, transient signals, such as voltage or current spikes, may damage the processor circuitry and/or other systems that are in contact with the detection circuitry. Component failure in the detection circuits may cause a hazardous condition within the indication or alarm circuits which may be in close proximity to an operator.
Finally, the voltage detection circuit described in the '215 patent may lack indication capability of high-voltage conditions associated with the electric machine, and self-test and diagnostic functions that are necessary to monitor the operation status of the detection circuit.
The disclosed high-voltage indication system is directed towards overcoming one or more of the problems set forth above.